In the letter, posted on her Facebook page, Beyoncé wrote: 'To my dearest fans in Antwerp. I've never postponed a show in my life. It was very hard for me. I promise I will make it up very son. I'm sorry if I disappointed you.

'Thank you for your concern. I'm feeling much better now, and I'm ready to give you a great show. See you tonight. All my love, Beyoncé.'

The handwritten letter went down well with fans, who praised the singer, referencing Rihanna's lack of apology after cancellations of multiple shows.

Beyoncé's cancellation comes amid reports the singer is expecting her second child with husband Jay Z.

Pregnant? The cancellation comes amid reports Beyoncé is pregnant after she was seen sporting an uncharacteristically rounded stomach

The New York Post newspaper claims 'multiple sources' told them Beyonce is pregnant following her attendance at the star-studded Met Ball last week, where the star's rumoured pregnancy was the talk of the night.

The pop superstar is said to have 'carefully' hidden her baby bump in a high-waisted Givenchy gown, but multiple photos have since surfaced of Beyonce sporting a growing stomach on her 65-date Mrs Carter Show world tour, which touched down in Dublin, Ireland, on Sunday.

Pictures of her on stage in London appear to show an uncharacteristically rounded tummy.

The Grown Woman singer welcomed her first child, daughter Blue Ivy Carter, into the world in January 2012.

Baby number two? Beyoncé's Met Gala look was reportedly designed to conceal her growing tummy

Beyoncé and Jay-Z - real name Shawn Carter - remained tight-lipped about her first pregnancy until sensationally announcing it live at the MTV Video Music Awards in August 2011.

Beyoncé recently admitted she would love to give her 18-month-old daughter a sibling, because she enjoyed such a close relationship with her younger sister Solange Knowles, 26, when they were growing up.

She said: 'I would like more children. I think my daughter needs some company. I definitely love being a big sister.'

Ubiquitous: The star is everywhere at the moment, while touring the world with her Mrs Carter, her H&M ads have been springing up across the world

Who runs the world? The star, unfazed by criticism, is on the European leg of the tour before moving on to North America

When pressed on when she may have another child, she added: 'At some point, when it's supposed to happen.'

However a source tells People magazine the baby may not be on the way just yet: 'Beyonce and Jay are planning for another baby after her tour is over and things calm down just a bit.'

Meanwhile, it has been revealed that Beyoncé's sister Solange is starting her own imprint record label.The imprint, entitled Saint Records, will be distributed through Sony.

Announcing the news, Solange wrote on Twitter: 'I’ll be releasing my full length album, and also future music projects that I’m excited about sharing.'

Baby daddy: Jay-Z and Beyoncé welcomed their daughter into the world in January 2012